The current standard of care for the treatment of diffuse large B cell lymphoma (DLBCL) includes anthracycline-based chemotherapy regimens such as CHOP in combination with the administration of the anti-CD20 monoclonal antibody Rituximab. This combination regimen (R-CHOP) can cure about 60% of patients and has improved the overall survival of DLBCL patients by 10-15% (Coiffier et al., N. Engl. J. Med, 346: 235-42 (2002)). Nonetheless, the molecular basis of response or resistance to this therapy is unknown.
DLBCL is a molecularly heterogeneous disease (Staudt et al., Adv. Immunol., 87: 163-208 (2005)), and different molecular subtypes of DLBCL can have very different prognoses following treatment. For example, gene expression profiling has identified two molecular subtypes of DLBCL that are biologically and clinically distinct (Rosenwald et al., N. Engl. J. Med., 346: 1937-47 (2002); Alizadeh et al., Nature, 403: 503-11 (2000)). The germinal center B cell-like (GCB) DLBCL subtype likely arises from normal germinal center B cells, whereas the activated B cell-like (ABC) DLBCL subtype may arise from a post-germinal center B cell that is blocked during plasmacytic differentiation. Many oncogenic mechanisms distinguish these subtypes: GCB DLBCLs have recurrent t(14,18) translocations, whereas ABC DLBCLs have recurrent trisomy 3 and deletion of the INK4a/ARF locus as well as constitutive activation of the anti-apoptotic NF-kB signalling pathway (Rosenwald et al., N. Engl. J. Med., 346: 1937-47 (2002); Bea et al., Blood, 106: 3183-90 (2005); Tagawa et al., Blood, 106: 1770-77 (2005); Davis et al., J. Exp. Med., 194:1861-74 (2001); Ngo et al., Nature, 441: 106-10 (2006); Lenz et al., Science, 319: 1676-79 (2008)). When treated with CHOP-like chemotherapy, the overall survival rates of patients with GCB DLBCL and ABC DLBCL were 60% and 30%, respectively (Wright et al., Proc. Nat'l. Acad. Sci. USA, 100: 9991-96 (2003)). Thus, the prognosis for different DLBCL can vary widely.
A separate analytical approach identified four gene expression signatures that reflect distinct DLBCL tumor attributes and that were associated with distinct survival profiles in CHOP-treated DLBCL patients (Rosenwald et al., N. Engl. J. Med., 346: 1937-47 (2002)). A “germinal center B cell” (GCB) signature was associated with a favorable prognosis and paralleled the distinction between ABC and GCB DLBCL. The “proliferation” signature was associated with an adverse prognosis and included MYC and its target genes. The “MHC class II” signature was silenced in the malignant cells in a subset of DLBCL cases, an event that was associated with inferior survival (Rosenwald et al., N. Engl. J. Med., 346: 1937-47 (2002); Rimsza et al., Blood, 103: 4251-58 (2004)). A fourth prognostic signature, termed “lymph node” signature was associated with favorable prognosis and included components of the extracellular matrix, suggesting that it reflects the nature of the tumor-infiltrating non-malignant cells. These signatures predicted survival in a statistically independent fashion, indicating that multiple biological variables dictate the response to CHOP chemotherapy in DLBCL.
Reports have suggested that the benefit of Rituximab immunotherapy might be restricted to certain molecular subtypes of DLBCL. High expression of BCL-2 or low expression of BCL-6 was associated with inferior survival with CHOP therapy. However, this distinction disappeared with R-CHOP therapy (Mounier et al., Blood, 101: 4279-84 (2003); Winter et al., Blood, 107: 4207-13 (2006)). Immunohistochemistry has also been used to distinguish DLBCLs with a germinal center versus post-germinal center phenotype. Although such immunohistochemical phenotypes were prognostically significant in CHOP-treated cases, they were not prognostic for R-CHOP-treated cases (Nyman et al., Blood, 109: 4930-35 (2007)).
Accordingly, there is a need for new methods of distinguishing among DLBCL subtypes that is prognostically significant for R-CHOP-treated patients.